It is common practice in the management of torque distribution in a power transmission mechanism to employ over-running couplings, acting alone or in combination with a friction coupling, for the purpose of establishing and disestablishing torque transfer from one torque transfer member to another or for anchoring a torque transfer member to a stationary housing, thereby providing a reaction point as torque is delivered from a torque input member to a driven member. In the case of a geared power transmission mechanism, for example, plural torque delivery paths are established for transfer of torque from a source of torque, such as an internal combustion engine, to a driven member such as a torque output shaft connected to a driving axle for a wheeled vehicle.
Such over-running couplings may include concentric inner and outer clutch or brake races with tiltable sprag elements disposed within the races for torque transfer from one race to the other when torque is delivered in one direction through the mechanism. Upon a torque reversal, the sprag elements will permit free-wheeling motion of one race with respect to the other. Another common overrunning coupling assembly comprises concentric inner and outer races, one of the races being cammed. Coupling rollers are disposed between the races, each roller engaging a separate cam surface. Upon torque distribution in one direction through the coupling, the rollers engage the cam surfaces; but upon a torque reversal, the rollers are allowed to disengage their respective cam surfaces as relative over-running motion of the races is permitted.
An objective of the invention is to provide an over-running coupling assembly that does not require precision machining operations that would be inherent in the manufacture of conventional sprag-type couplings or over-running roller coupling assemblies. Planar coupling plates are described in co-pending patent application Ser. No. 08/382,070, filed Feb. 1, 1995 and now U.S. Pat. No. 5,597,057. Reference may be made to that pending patent application for the purpose of supplementing our present invention disclosure. The co-pending application is assigned to the assignee of our present invention.
It is a further objective of the invention to avoid high stress and wear problems that might be associated with prior art planar disk-type clutches such as those disclosed in U.S. Pat. No. 5,070,978 wherein a drive plate and a driven plate of a planar clutch assembly are disposed in closely-spaced, juxtaposed relationship and adapted for rotation about a common axis, one plate being connected to a driving shaft and the other being connected to a driven shaft. A plurality of pockets or recesses is formed in the one clutch plate at angularly spaced locations that are positioned at a predetermined radius from the axis. Corresponding pockets or recesses are formed in the other clutch plate, each pocket thereof having disposed therein a pawl or strut adapted for tilting movement. One edge of each pawl is adapted to register with a pocket formed on the one clutch plate, thereby causing the torque input member to drive the torque output member in a driving direction. If the direction of relative rotation of the clutch plates is reversed, the pawls will disengage the pockets in the one plate thereby allowing free-wheeling motion of the driving member with respect to the driven member. Means may be provided for normally urging each pawl individually into locking engagement with a pocket formed in the one clutch plate.
As described in the co-pending patent application, it is desirable to prevent floating of the individual struts. They are pivotally mounted in the strut pockets in which the struts are received so that the individual struts will be prevented from floating when one clutch plate rotates relative to the other at relatively high relative speeds. Such a floating condition may induce premature wear of the strut and the clutch plates, particularly in those instances when it is undesirable or impractical to lubricate the juxtaposed faces of the clutch plates with a large quantity of lubricating oil during operation.
The struts of a design such as that described in the co-pending application include ear portions that are received in the strut pockets, and provision is made for establishing a pivoting action of each strut one margin. The stresses that are induced in the struts that transfer torque from the driving member to the driven member, however, can be extreme, particularly where tolerance variations between the struts and the cooperating pockets of the driven plate are such that a greater load is carried by one strut relative to a companion strut.
It is desirable further for the struts to be capable of being displaced radially inward under the influence of a hydrodynamic boundary layer, during free-wheeling operation of the clutch. The boundary layer establishes a hydrodynamic bearing that prevents ratcheting action of the struts as the latter traverse the pockets of the driven member during relative overrunning motion of the coupling plates.